Osmotic systems for delivering a beneficial agent to an environment of use are known to the art in U.S. Pat. Nos. 3,845,770 and 3,916,899. The systems disclosed in these patents comprise a semipermeable wall that surrounds a compartment containing an agent. The wall is permeable to an external fluid, substantially impermeable to agent, and there is a passageway through the wall for delivering the agent from the system. These systems release agent by fluid being imbibed through the wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall to produce a solution of soluble agent, or a solution of an osmotic attractment containing an agent that has limited solubility in the fluid, which solution in either operation is dispensed from the system. These systems are extraordinarily effective for delivering both an agent that is soluble in the fluid, and for delivering an agent that has limited solubility in the fluid and is admixed with an osmotically effective compound that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid. While the above systems are outstanding and represent a pioneer advancement in the delivery art, and while they are endowed with ideal kinetics useful for delivering numerous beneficial agents, there is an occasional instance where the kinetics of the system can be unexpectedly improved to lead to more desirable results. For example, the rate of agent delivered by the system is constant for most agents as long as excess solid agent is present in the system with its rate declining parabolically toward zero as the agent's concentration decreases below saturation. That is, both the solubility and the density of the agent influence the amount of agent delivered at a constant rate, and that amount delivered at a declining rate is proportional to the solubility of the agent and inversely proportional to its density. These actions often make it difficult to deliver substantially all of the agent at a constant rate and thereby obtain the full benefit of the agent's therapeutic effect, particularly when the agent is very soluble or practically insoluble in the fluid and concomitantly a portion of the agent cannot be delivered at a constant rate. The present invention enhances the amount of these latter agents delivered at a constant and controlled rate over time by using a volume amplifier to improve kinetics and the amount of agent delivered from the system. The system with the amplifier also can optionally deliver increased amounts of very soluble or practically insoluble agents as pure agents substantially free of any osmotically effective compounds being mixed therewith. A mathematical presentation pertaining to the instant subject matter is known in J. Pharm. Sci., Vol. 64, No. 12, pages 1987 to 1991, 1975.